Programmable device

ABSTRACT

A programmable device including a source-drain-gate structure. The device includes two programming electrodes and an antiferromagnetic multiferroic material between the two programming electrodes for switching the spontaneous polarization between a first spontaneous polarization direction and a second spontaneous polarization direction. The programmable device further includes a ferromagnetic material, which is in immediate contact with the multiferroic material. Magnetization of the ferromagnetic material is switchable by a transition between the first switching state and the second switching state of the multiferroic material by an exchange coupling between electronic states of the multiferroic material and the ferromagnetic material. The programmable device also includes means for determining a direction of the magnetization of the ferromagnetic material. A spin valve effect is used for causing an electrical resistance between the source and the drain electrode.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. 119 from EuropeanPatent Application 08104301.0, filed Jun. 6, 2008 and from EuropeanPatent Application 08104303.6, filed Jun. 6, 2008, the entire contentsof both of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to programmable devices and, moreparticularly, to a memory element containing a plurality of suchprogrammable devices and a logic circuit containing such programmabledevices.

2. Description of Related Art

Memory and logic devices such as complementary metal-oxide-semiconductor(CMOS) are major classes of integrated circuits. They are used inprocessor and memory chips such as microprocessors, microcontrollers,solid-state stand-alone and embedded memory circuits and other digitallogic circuits.

The most widely used memory technologies are DRAM, SRAM, Floating gate(Flash), and MRAM. These existing technologies can not be integratedwith high areal density and provide at the same time non-volatile andfast operation. In particular, Flash is too slow for many embeddedapplications, SRAM and DRAM loose their memory state when disconnectedfrom a power supply, and SRAM and MRAM can only be manufactured with alimited areal density. In addition, the high programming voltage ofFlash complicates integration with CMOS circuitry.

The logic state of CMOS is volatile and the input voltage has to bemaintained. Always maintaining the input voltage will lead toconsiderable power consumption and heating in future CMOS generations.

WO 2007/110950 proposes the use of ferromagnetic multiferroic materialsfor building memory devices. However, such devices suffer fromdisadvantages. For example, currently no multiferroics are known thatpossess ferroelectric and ferromagnetic ordering at room temperature.Further, such devices would not be suited for significantminiaturization because below a certain size the superparamagnetic limitis reached. The term “superparamagnetic limit” is the size at which themagnetic anisotropy of a magnetic layer in a cell becomes comparable tokT, where k is Boltzmann's constant and T is the absolute temperature.The magnetization becomes unstable below that limit.

SUMMARY OF THE INVENTION

A programmable device according to a first embodiment of the presentinvention includes: a source electrode; a drain electrode; and a gatemade of antiferromagnetic multiferroic material. The gate is switchableby application of an electrical signal between a first switching statewith a first spontaneous polarization direction and a second switchingstate with a second spontaneous polarization direction. A first materialselected from the group consisting of ferromagnetic material andferrimagnetic material is in immediate contact with the multiferroicmaterial. A magnetization of the first material is switchable by atransition between the first switching state and the second switchingstate of the multiferroic material by an exchange coupling betweenelectronic states of the multiferroic material and the first material.The device further includes means for determining a direction of themagnetization of the first material.

According to another embodiment, the device of the present inventionincludes: a source electrode; a drain electrode; a gate made of amultiferroic material; an electrical resistance between the sourceelectrode and the drain electrode providing a current path via a channelregion. The electrical resistance is switchable by application of anelectrical signal to the gate, the current path provides a junctionbetween a channel region material and a current path ferromagneticmaterial, and the electrical resistance between the source electrode andthe drain electrode is switchable due to a spin valve effect so that aswitching state of the multiferroic material influences a relativeorientation of magnetic moments of charge carriers flowing across thejunction and a magnetization of the current path ferromagnetic material.

In other embodiments, groups of the above devices are used to createlogic elements and memory elements.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings are all schematic and not to scale. In the drawings, samereference numerals in different figures refer to same or correspondingelements.

FIGS. 1 a and 1 b show cross sections through a first embodiment of aprogrammable device in two switching states.

FIGS. 2 a and 2 b show cross sections through a second embodiment of aprogrammable device in two switching states.

FIGS. 3 a and 3 b show cross sections through a third embodiment of aprogrammable device in two switching states.

FIGS. 4 a and 4 b show cross sections through a fourth embodiment of aprogrammable device in two switching states.

FIGS. 5 a and 5 b show cross sections through a logic device comprisingtwo programmable devices in two switching states.

FIGS. 6 a and 6 b show yet another alternative embodiment of aprogrammable device according to the present invention in two switchingstates.

FIG. 7 shows a top view of the arrangement of FIGS. 6 a and 6 b.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention provides a programmable device capable of servingas building blocks for memory and logic elements overcoming thedrawbacks of prior art memory and logic cells. In particular, theprogrammable device is non-volatile, and in addition makes high arealdensity and/or fast operation possible.

Ferroelectric materials possess a spontaneous polarization that isstable and can be switched hysteretically by an applied electric field.Multiferroic antiferromagnets possess simultaneous ferroelectric andantiferromagnetic ordering. These two order parameters are coupled.

The multiferroic material is therefore programmable by application of anelectrical signal, for example by the application of an electric fieldpulse, across it. Due to the coupling of the antiferromagnetic orderparameter to the ferroelectric order parameter, the antiferromagneticorder parameter is also programmable. Due to the exchange coupling ofthe antiferromagnet to the ferromagnetic material, the magnetizationdirection of the ferromagnetic material is also switched.

The means for determining a direction of the magnetization of theferromagnetic material may, according to one preferred embodiment, bebased on a spin valve effect. To this end, an electrical resistancebetween the source and drain electrodes and across a channel regionbetween them is switchable by the ferromagnetic material. The currentpath between the source electrode and the drain electrode includes ajunction between a channel region material and ferromagnetic material,for example of the drain electrode. In general, the ferromagneticmaterial of the drain (or source) electrode or of the otherferromagnetic element in the current path is called current pathferromagnetic material. The spin valve effect may then be used in one ofthe following two configurations.

-   -   (i). The current path ferromagnetic material (which may be, for        example, a drain electrode ferromagnetic material) has a fixed        magnetization and serves as ferromagnetic detector, whereas the        gate ferromagnetic material in immediate contact with the        multiferroic material causes a stray field influencing the        magnetic moment's orientation of charge carriers flowing in the        channel region. Herein, the terms “gate ferromagnet”,        “ferromagnet”, “ferromagnetic layer” and “ferromagnetic        material” include ferrimagnetic material, those skilled in the        art recognizing that the stray field producing function of        ferromagnets can also be fulfilled by a ferrimagnet.    -   (ii). The current path ferromagnetic material is the        ferromagnetic material in immediate contact with the        multiferroic material. The charge carriers flowing in the        channel region have a fixed preferred orientation because, for        example, they are oriented by a stray field of a fixed direction        ferromagnet or because they are injected from a ferromagnetic        injector (source).

The programmable device features the advantage of being non-volatilebecause the ferroelectric and magnetic order parameters of themultiferroic material are non-volatile. Due to its non-volatilecharacter, low power consumption can be expected.

Also, changing the ferroelectric polarization of a multiferroic elementis an inherently fast process (50 ps). The programmable device accordingto the present invention therefore has a significant programming speedadvantage compared to flash memory (1 μs).

Depending on the measuring method, the programmable device can beimplemented in a simple, small unit cell (having a required space ofonly 6F² in a one transistor structure without any additional resistorsor capacitors) and thus is suitable for integration with higher arealdensity than prior art programmable devices. Also, it scales well whengoing to smaller cells, because it does not include any capacitors.

A further advantage of the programmable device, especially compared toMRAM, is a reduced write energy of about 10⁻¹⁵ J/bit versus 10⁻¹¹ J/bitfor MRAM.

A still further advantage of the programmable device, especiallycompared to Flash, is a lower programming voltage of around 1 V versus15 V for Flash.

With the present invention, the more temperature stableantiferromagnetic multiferroics can be used. Also, there is theadvantage that the superparamagnetic limit is not a concern inantiferromagnets, so the cell may be designed to be comparably smallerand still be stable.

An example of a useable antiferromagnetic multiferroic material suitablefor the present invention is BiFeO₃.

Among the usable ferromagnetic multiferroics are Boracite (Ni₃B₇O₁₃I),Perovskites like BiMnO₃ and TbMnO₃, and Sulfates such as CdCr₂S₄. Inthese currently known materials, the coupled order parameters arenon-zero at low temperatures only, so the programmable device andelements made therewith are primarily suited for special applicationswhere cooled devices are acceptable. This embodiment of the presentinvention will increase in usability with multiferroic ferromagneticmaterials that are stable at and above room temperature.

According to an embodiment, the multiferroic material is a multiferroicantiferromagnet coupled (in general by exchange bias coupling) to eithera gate ferromagnet or to the drain (or source) electrode, pinning thesame. This “ferromagnet pinning” embodiment features the advantage thatknown antiferromagnetic multiferroics are more temperature stable thantheir ferromagnetic counterparts. Also, there is the advantage that thesuperparamagnetic limit (i.e. the size at which the magnetic anisotropyof a magnetic layer in a cell becomes comparable to kT, where k isBoltzmann's constant and T is the absolute temperature, so that themagnetization becomes unstable below that limit) is not an issue inantiferromagnets, so the cell may be designed to be comparatively smalland still be stable.

The programmable device according to the present invention can be usedboth as a memory cell of a memory device and as a logic element of alogic circuit. If the conducting channel is semiconducting (doped orundoped), the programmable device can be used in the manner of aconventional FET as well as, for example, select-transistor for the readoperation.

The programmable device according to an embodiment of the presentinvention comprises a source-drain-gate functional structure (this doesnot imply that the physical design necessarily has to be similar to theone of a field effect transistor), i.e. a source electrode and a drainelectrode between which a channel region is established, where chargecarriers can flow between the source and the drain electrode, dependenton the application of an electrical signal to the gate. The channelregion can, as is known in the art, be an electrical conductor,semiconductor or insulating material (thus including comparably few freecharge carriers) or be doped to be conducting; the configuration of thechannel region is not essential for the present invention. The gatecomprises a multiferroic material, thus a material with at least twocoupled order parameters. According to one preferred embodiment of thepresent invention, a spin valve effect is used for causing an electricalresistance between the source and the drain electrode (for an electricalcurrent flowing in at least one direction between the source and drainelectrode) to be switchable. To this end, preferably the drain electrode(and/or the source electrode in case of p-type conduction) isferromagnetic. As an alternative to the drain electrode (and/or sourceelectrode) being ferromagnetic, another element on the current pathbetween the source and the drain contacts may be ferromagnetic, wherebya junction between a non-ferromagnetic material and a ferromagneticmaterial is present, which can exhibit a spin valve effect. In general,the ferromagnetic material of the drain (or source) electrode or of theother ferromagnetic element in the current path is called “current pathferromagnetic material”.

The multiferroic material generally is arranged between two electrodes,one of which belongs to the gate, between which a voltage can be appliedso that the ferroelectric spontaneous polarization can be oriented. Themultiferroic material is capable of influencing the relative orientationof the magnetic moments of charge carriers flowing to the drainelectrode and of a magnetization of the drain electrode (or othercurrent path ferromagnetic material). This means that the multiferroicmaterial can either produce a magnetic field influencing the magneticmoments of the charge carrier flowing in the conducting channel, or canswitch the magnetization direction of the drain electrode magnetization.

Using the present invention, memory and logic circuits can be integratedwithout additional mask steps, thus providing a manufacturing costadvantage for such integrated circuits.

In the ferromagnetic materials of elements depicted in the figures,filled arrows generally indicate fixed magnetizations, magnetizationsthat are pinned in some way, that have a coercive field that is higherthan the sum of effective fields acting on them during normal operationor that are otherwise influenced not to change a magnetization directionduring normal operation of the programmable device. Open arrows indicatemagnetizations that are switchable by the programming voltage pulsesignals.

Referring to FIGS. 1 a and 1 b, a programmable device 1 includes, on asubstrate 3, a source electrode 12 and a drain electrode 13, both of aferromagnetic electrically conducting material, for example of a Cobaltalloy or Permalloy (an FeNiCo alloy). Between the source and drainelectrodes, a conducting channel 21 is formed, for example by an n-dopedregion in the substrate or in any other suitable manner; the conductingchannel may, but need not, include the same material as the substrate 3.

The substrate may be any suitable substrate, such as a semiconductingsubstrate, for example Gallium Arsenide or Silicon. The substrate in thedepicted embodiment is contacted by a reference voltage contact, namelya ground contact 8 (or “bulk” contact). As is known in the art, theremay be a contact or connection (not shown) between, for example, thesource electrode 12 and the ground contact 8, so that the former isalways at ground potential (or another reference potential as the casemay be).

The programmable device 1 further includes a gate that includes a gateelectrode 17, a ferromagnetic layer 14 of any ferromagnetic electricallyconducting material, and an antiferromagnetic multiferroic layer 15sandwiched between the gate electrode and the ferromagnetic layer. Theferromagnetic layer is insulated by a dielectric layer 16 from thesource and drain electrodes 12, 13 and from the conducting channel 21.

A programming voltage 20 may be applied between the ferromagnetic layer14 and the gate electrode 17. As a result, the spontaneous polarizationof the multiferroic material may be switched between a first and asecond state depicted in FIGS. 1 a and 1 b, respectively. Because thematerial is multiferroic, the switching of the ferroelectric spontaneouspolarization also switches the according antiferromagnetic orderparameter, for example by reversing the sequence of “up” and “down”magnetized layers in the multiferroic material. The ferromagnetic layer14, being immediately adjacent to the multiferroic layer 15, is exchangecoupled to the multiferroic layer. Due to this, the switching of theferroelectric spontaneous polarization of the multiferroic layer 15 hasthe effect of also switching the magnetization direction of theferromagnetic layer 14.

In FIGS. 1 a and 1 b, source electrode 12 functions as a ferromagneticinjector (in the case of n-type conduction), and the drain electrode 13as a ferromagnetic detector. The stray field of the ferromagnetic layer14 influences the charge carriers (symbolized by small arrows depictingthe charge carriers' magnetic moments in the figures).

In FIG. 1 a, the magnetization of the ferromagnetic layer 14 is parallelto the magnetization of the source electrode 12. The magnetic moment ofthe majority of the charge carriers is therefore oriented parallel tothe magnetic field produced by the ferromagnetic layer and acting onthem. The majority charge carriers therefore maintain their magneticmoment when propagating in the direction of the block arrow in FIG. 1 a.The magnetization of the drain electrode 13 is now chosen to be suchthat the charge carriers with the maintained magnetic moment can easilyenter the drain electrode. The programmable device in the configurationof FIG. 1 a is in the “open” state.

In contrast thereto, in FIG. 1 b the programming voltage 20 of theinverse polarity causes the magnetization of the ferromagnetic layer tobe oriented in the direction opposite to the direction depicted in FIG.1 a. The majority of the charge carriers injected by the sourceelectrode 12 have a magnetic field oriented antiparallel to the magneticstray field produced by the ferromagnetic layer 14, so that the magneticmoment is reversed on the path from the source electrode to the drainelectrode. Due to the electronic structure of the magnetized drainelectrode, however, the charge carriers encounter an energy barrier (forexample for having to again flip their magnetic moment) when enteringthe drain electrode material. This energy barrier effect, called “spinvalve effect,” is similar to the effect that is also responsible for“giant magnetoresistance” or “tunneling magnetoresistance” and isdescribed in literature.

Because this energy barrier causes a higher electrical resistancecompared to the “open” state, the programmable device in FIG. 1 b is inthe “closed” state.

In applications where the programmable device is a memory element, the“open” and “closed” states will often be referred to as “0” and “1”;this holds for all embodiments.

Note that in the described embodiment, the configuration where thecharge carrier magnetic moment is parallel to the drain (ferromagneticdetector), electrode magnetization is assumed to be the configurationwith the small energy barrier and low resistance, whereas theantiparallel configuration is the one with the high energy barrier andhigh resistance. This need not be the case. Rather, depending on theband structure of the drain electrode material, the opposite can betrue, for example, if the drain electrode material comprises a so-called“strong” ferromagnet where there are no free states for charge carriersin the majority band.

As for all other embodiments, in the case of p-type conduction, wherethe charge carriers may be viewed as “holes” instead of electrons, theroles of the source and drain contacts may be interchanged, but theprinciple remains the same.

The programming voltage may optionally be applied as only a programmingpulse. Because of the non-volatile nature of the switching state in amultiferroic material, the state is retained even when the power supplyis disconnected.

The programmable device 1 of FIGS. 2 a and 2 b (showing, in analogy toFIGS. 1 a and 1 b, the open and closed states, respectively) isdifferent from the one of FIGS. 1 a and 1 b in that the sequence of themultiferroic layer 15 and of the ferromagnetic layer 14 is reversed. Themultiferroic layer 15 is sandwiched between the ferromagnetic layer 14on one side and the conducting channel 21 and the source and drainelectrodes on the other side. The dielectric layer 16 then is notnecessary any more because the multiferroic material 15, in contrast tomost of the commonly used ferromagnetic materials, is electricallyinsulating.

Also, a separate gate electrode layer 17 is optional and not shown inthe drawings, since the ferromagnetic layer 14 can optionally serve asthe gate electrode.

In FIGS. 2 a and 2 b, the programming voltage 20 may be applied betweenthe gate electrode (ferromagnetic layer 14) and the source electrode 12or the drain electrode 13. In contrast to FIGS. 1 a and 1 b, no separatecontact (the fifth contact, if the “bulk” electrode is also counted) forthe ferromagnetic layer is needed. The stray magnetic field produced bythe ferromagnetic layer 14 impinges on the charge carriers flowing inthe conducting channel 21 through the multiferroic material 15 insteadof through the dielectric material 16. Apart from this difference, thefunctioning principle is analogous to the one of FIGS. 1 a and 1 b.

Although in FIGS. 1 a-2 b, the source electrode 12 functions as a spininjector injecting charge carriers with magnetic moment orientationparallel to the magnetization of ferromagnetic layer 14 when the deviceis in the “open” state, this need not be the case. Rather, it is alsopossible to have the situation where the source electrode injects chargecarriers with magnetic moment antiparallel to the to the magnetizationof ferromagnetic layer 14 when the device is in the “open” state. Thenthe magnetic moments are reversed along the path from the sourceelectrode to the drain electrode in the “open” state and maintain theirorientation in the “closed” state.

Referring to FIGS. 3 a and 3 b, yet another alternative, in whichunpolarized charge carriers are injected, is shown. In any case, the“open” and “closed” states are distinct in that the magnetic moments ofa majority of charge carriers encounters and a magnetization of thedrain electrode are oriented relative to one another so that the chargecarriers encounter a higher resistance when entering the drain electrodein the closed state than in the open state.

The embodiment of FIGS. 3 a and 3 b (showing, in analogy to FIGS. 2 aand 2 b, the open and closed states of the programmable device 1,respectively) is distinct from the one of FIGS. 2 a and 2 b in that thesource electrode 12 is not ferromagnetic but injects essentiallyunpolarized charge carriers. The magnetic moments of the charge carriersare then aligned while transiting the conducting path. The spin valveeffect works in the same way as in the above-described embodiments.

The principle of non-polarized spin injection may also be used incombination with all other embodiments, thus including the structures ofFIGS. 1 a, 1 b, and of FIGS. 4 a, 4 b, and 6 a, 6 b described below.

Another embodiment of a programmable device 1 is shown in FIGS. 4 a and4 b (again showing, in analogy to FIGS. 2 a and 2 b, the open and closedstates of the programmable device 1, respectively). In thisconfiguration, the ferromagnetic drain electrode 13 is switchable, i.e.has a magnetization the direction of which is switchable. To this end,the drain electrode is in direct contact with the multiferroic material15 and exchange coupled to it. The effective coercivity of the drainelectrode 13 magnetization is smaller than the effective exchangecoupling.

The ferromagnetic layer 14 producing the stray field for influencing theorientation of the magnetic moments has a fixed magnetization. Forexample, a preferably electrically insulating spacer layer (not shown)between the multiferroic material 15 and the ferromagnetic layer 14 mayimpede an exchange coupling between the ferromagnetic layer and themultiferroic material. In addition or as an alternative, theferromagnetic layer may be “pinned,” i.e., its magnetization may befixed, for example by an exchange coupling (not shown) to a further, forexample, antiferromagnetic layer on top if it. Alternatively, theferromagnetic layer may be magnetically hard, i.e. have a highcoercivity.

In contrast to the previously described embodiments, the charge carriersin the embodiment of FIGS. 4 a and 4 b are not subject to different spinrotation in the open and closed states. Rather, the ferromagneticdetector changes its sensitivity by having its magnetization switched.The spin valve effect causes, in analogy to the embodiments shown in theother figures, the electrical resistance to be different between the“open” state (FIG. 4 a) and the “closed” state (FIG. 4 b).

Referring to FIGS. 5 a and 5 b, a logic element 51 similar to a CMOSinverter can be formed combining two programmable devices 1, 1′according to the present invention. For reasons of simplicity, it isassumed that the resistance in the closed state is larger than theresistance in the open state by orders of magnitude (thus “R=∞” in theclosed state, and “R=0” in the open state; in physical reality thiswill, of course, be achieved only approximately).

In the depicted embodiment, two programmable devices as describedreferring to FIGS. 2 a and 2 b are used. The ferromagnetic detectormagnetization (the drain electrode 13, 13′ magnetization) of the twoprogrammable devices of the logic element is oriented antiparallel withrespect to each other. The gate electrodes of the two programmabledevices are connected in parallel, and the drain electrode 13 of thefirst programmable device is in electrical contact with the sourceelectrode 12′ of the second programmable device and with an outputterminal 52. The source electrode of the first programmable device 1 isconnected to a first voltage (−V_(DD)), and the drain electrode of thesecond programmable device 11 is connected to a second voltage(+V_(DD)),

Depending on the polarity of the input voltage, either the first voltage(FIG. 5 a) or the second voltage (FIG. 5 b) will be connected to anoutput port 52. Once the magnetization of the ferromagnetic gate layersis set by the input voltage across the multiferroic layer, the outputretains its logic state even when the power supply is disconnected.

An even further embodiment of a programmable device 1 according to thepresent invention is depicted in FIGS. 6 a, 6 b, and 7. FIGS. 6 a and 6b show the open and closed switching states, respectively. Thisembodiment differs from the previously described embodiments in that theHall effect instead of the spin valve effect is used for determining thedirection of the magnetization of the gate ferromagnet 14. Embodimentsof programmable devices based on this effect or TunnelingMagnetoresistance/Giant Magnetoresistance or on a movable probe areprimarily useable as memory elements, whereas applications for logicelements are less manifest.

In the embodiment of FIGS. 6 a and 6 b, if a current flows between thesource and drain electrodes, the stray field produced by the gateferromagnet 14, because of the Hall effect, produces an electricalvoltage in the direction perpendicular to both, the current directionand the magnetic field direction. This electrical voltage may bemeasured by additional electrodes 61, 62.

A magnetic tunneling junction to a fixed-magnetization ferromagnet (thusa thin insulating layer and a fixed-magnetization (pinned) ferromagnetatop the gate ferromagnet 14 in the arrangement of FIGS. 6 a, 6 b) wouldbe yet another alternative means for measuring the magnetizationdirection of the gate ferromagnet.

Various other embodiments may be envisioned. For example, in the “spinvalve” embodiments, the spin valve effect does not rely on the magneticmoments being, in the “open” state, parallel (or antiparallel) to thecurrent path ferromagnetic material. As an alternative, they may have amagnetic moment that is at an angle (such as orthogonal) to the currentpath ferromagnetic material magnetization and still encounter arelatively low energy barrier at the junction. Also in the other(closed) state, the magnetic moments need not be exactly antiparallel asillustrated, for simplicity, in the above embodiments, but may beapproximately antiparallel or similar. Depending on the current path(for example drain electrode) ferromagnetic material, the “closed” statemay even correspond to the state with parallel magnetizations (see theabove remark on “strong” ferromagnets). The general principle is thatthe switching influences a relative orientation of the orientation ofmagnetic moments of charge carriers flowing across the junction and amagnetization of the current path ferromagnetic material, and that theelectrical resistance between source and drain electrodes differsbetween the two switching states because of this relative orientationchange.

While the present invention has been described with reference topreferred embodiments thereof, those skilled in the art will recognizethat the above and other changes in form and details may be made withoutdeparting from the spirit and scope of the present invention as definedin the following claims.

1. A programmable device, comprising: a source electrode; a drainelectrode; a gate having an antiferromagnetic multiferroic material,said gate being switchable by application of an electrical signalthereto between a first switching state with a first spontaneouspolarization direction and a second switching state with a secondspontaneous polarization direction; a first material selected from thegroup consisting of ferromagnetic material and ferrimagnetic material,said first material being in immediate contact with the multiferroicmaterial, a magnetization of the first material being switchable by atransition between the first switching state and the second switchingstate of the multiferroic material by an exchange coupling betweenelectronic states of the multiferroic material and the first material;and means for determining a direction of the magnetization of the firstmaterial; wherein: transitions between the first and second switchingstates cause an electrical resistance between the source electrode andthe drain electrode across a channel region to switch; a current pathbetween the source electrode and the drain electrode includes a junctionbetween a channel region material and a current path ferromagneticmaterial; and the switching of the electrical resistance between thesource electrode and the drain electrode is due to a spin valve effect,wherein the switching state of the multiferroic material influences (i)a relative orientation of magnetic moments of charge carriers flowingacross the junction and (ii) a magnetization of the current pathferromagnetic material.
 2. The programmable device according to claim 1,wherein the current path ferromagnetic material is present in at leastone of the drain electrode and the source electrode, thus making the atleast one of the drain electrode and the source electrode ferromagnetic.3. The programmable device according to claim 1, wherein: the firstmaterial in immediate contact with the multiferroic material is either agate ferromagnet or a ferrimagnet arranged in the gate and is capable ofcausing a magnetic field to be impinge on charge carriers flowing in thechannel region.
 4. The programmable device according to claim 1, whereinthe first material in immediate contact with the multiferroic materialis the current path ferromagnetic material.
 5. The programmable deviceaccording to claim 4, further comprising: contacts for applying theelectrical signal between a gate contact and one of the sourceelectrode, the drain electrode, and a bulk contact.
 6. The programmabledevice according to claim 1, wherein the means for determining adirection of the magnetization of the first material comprises a Hallprobe.
 7. The programmable device according to claim 1, wherein themeans for determining a direction of the magnetization of the firstmaterial comprises either a tunnel magnetoresistance probe or a giantmagnetoresistance probe.
 8. A logic element, comprising: a firstprogrammable device according to claim 1; and a second programmabledevice according to claim 1; wherein: a portion of the firstprogrammable device has fixed magnetization direction and thecorresponding portion of the second programmable device has differentfixed magnetization direction; and the drain electrode of the firstprogrammable device and the source electrode of the second drainelectrode are electrically connected so that the electrical signal cansimultaneously be applied to the gates of the first and the secondprogrammable device.
 9. A logic circuit comprising a plurality of logicelements according to claim
 8. 10. A memory element, comprising: aplurality of programmable devices according to claim 1 serving as memorycells; a plurality of contacts for applying electrical signalsindividually to the gates of the programmable devices; and a pluralityof contacts for measuring an electrical resistance between the sourceand the drain electrode of an individually addressed programmable devicefor reading the memory device.
 11. A programmable device comprising: asource electrode; a drain electrode; a gate having a multiferroicmaterial; an electrical resistance between the source electrode and thedrain electrode providing a current path via a channel region, whereinthe resistance is switchable by application of an electrical signal tothe gate, wherein the current path comprises a junction between achannel region material and a current path ferromagnetic material, andwherein the electrical resistance between the source electrode and thedrain electrode is switchable due to a spin valve effect so that aswitching state of the multiferroic material influences (i) a relativeorientation of magnetic moments of charge carriers flowing across thejunction and (ii) a magnetization of the current path ferromagneticmaterial.
 12. The programmable device according to claim 11, wherein thecurrent path ferromagnetic material is present in at least one of thedrain electrode and the source electrode, making said at least one ofthe drain electrode and the source electrode ferromagnetic.
 13. Theprogrammable device according to claim 12, wherein both the sourceelectrode and the drain electrode are ferromagnetic, causing theprogrammable device to comprise a ferromagnetic injector for spinpolarized charge carriers.
 14. The programmable device according toclaim 13, wherein the gate further comprises a gate magnet, which isselected from the group consisting of a gate ferromagnet and a gateferrimagnet, capable of causing a magnetic field to be present in thechannel region, the magnetic field influencing an orientation of chargecarrier magnetic moments of charge carriers flowing in the channelregion and to the junction.
 15. The programmable device according toclaim 14, wherein the multiferroic material is a multiferroicantiferromagnet.
 16. The programmable device according to claim 15,wherein the gate magnet is coupled to the multiferroic antiferromagnet,a magnetization direction of the gate magnet being switchable by thecoupling to the multiferroic antiferromagnet due to the application ofthe electrical signal to the gate.
 17. The programmable device accordingto claim 16 further comprising a dielectric layer between the channelregion and the gate magnet, the gate magnet being a layer between themultiferroic antiferromagnet and the dielectric layer.
 18. Theprogrammable device according to claim 17, wherein the multiferroicantiferromagnet is arranged between the gate magnet and the channelregion.
 19. The programmable device according to claim 18, furthercomprising contacts for applying the electrical signal between the gatemagnet and one of the source electrode, the drain electrode, and a bulkcontact.
 20. The programmable device according to claim 19, wherein themultiferroic antiferromagnet is arranged immediately adjacent to thechannel region.
 21. The programmable device according to claim 16,wherein one of the drain electrode and the source electrode isferromagnetic and coupled to the multiferroic antiferromagnet, amagnetization direction of the drain electrode or source electrode beingswitchable by the coupling to the multiferroic antiferromagnet due tothe application of the electrical signal to the gate.
 22. Theprogrammable device according to claim 21, wherein the multiferroicmaterial is a multiferroic magnet selected from the group consisting ofa multiferroic ferromagnet and a multiferroic ferrimagnet and is capableof causing a magnetic field to be present in the channel region.
 23. Alogic element, comprising: a first programmable device according toclaim 11; and a second programmable device according to claim 11;wherein: a portion of the first programmable device has a first fixedmagnetization direction and the corresponding portion of the secondprogrammable device has a fixed second magnetization direction that isdifferent from the first magnetization direction; and the drainelectrode of the first programmable device and the source electrode ofthe second programmable device are electrically connected so that theelectrical signal can be simultaneously applied to the gates of thefirst and second programmable devices.
 24. A memory element, comprising:a plurality of programmable devices according to claim 11, eachprogrammable device serving as a memory cell; a plurality of contactsfor applying electrical signals individually to the gates of theprogrammable devices; and a plurality of contacts for measuring anelectrical resistance between the source and the drain electrode of anindividually addressed programmable device for reading the memorydevice.